The overall objectives of this ongoing investigation are elucidation of fundamental biological mechanisms involved in the formation, evolution, recombination, transfer, replication, and genetic expression of R factors --- and modification of these processes as a result of information obtained. Objectives during the year of proposed research include: continued study of physical and functional relationships between different R factors, and between R factors and other plasmids, by electron microscope heteroduplex techniques; investigation of the structural and genetic properties of biologically functional R-factor species constructed in vitro using restriction endonucleases and introduced into E. coli by the transformation procedure developed in this laboratory; studies of replication of hybrid plasmids constructed in vitro from plasmids having set modes of replication; investigation of the role of directly and inverse-repeated DNA sequences in plasmid recombination and in the control of genetic expression of R-factor genes.